The present invention generally relates to means and methods by which a target area is adequately illuminated by one or more lighting fixtures. More specifically, the present invention relates to improvements in the design and use of lighting fixtures such that the steps of aiming and cutoff of light projected from said lighting fixtures may be separated so to gain more flexibility in addressing the lighting needs of a particular application without adversely affecting the size, effective projected area, or efficiency of the lighting fixtures.
It is well known that to adequately illuminate a target area—particularly a target area of complex shape—a combination of light directing (e.g., aiming, collimating) and light redirecting (e.g., blocking, reflecting) efforts are needed; see, for example, U.S. Pat. No. 7,458,700 incorporated by reference herein. This concept is generally illustrated in FIGS. 1A-C for the example of a sports field illuminated by a plurality of elevated floodlight-type fixtures. As can be seen from FIG. 1A, in the un-aimed state a fixture 4 illuminates some portion of target area 5 (which typically comprises not only the horizontal plane containing the sports field, but also a finite space above and about said field); this illumination is diagrammatically illustrated by projected beam 7 wherein the hatched portion of beam 7 is considered desirable. Adjusting fixture 4 relative to pole 6 (e.g., by pivoting about its attachment point) aims beam 7 toward the leftmost portion of target area 5 as desired (see FIG. 1B), but also results in the lighting of undesired areas such as bleachers 515. This light, commonly referred to as spill light, is wasteful and a potential nuisance (e.g., to spectators in bleachers 515) or hazardous (e.g., to drivers on a road adjacent to target area 5). To adequately eliminate spill light, a visor or analogous device may be added to fixture 4 (see FIG. 1C) to provide a desired cutoff. Some visors, such as those disclosed in U.S. Pat. No. 7,789,540 incorporated by reference herein, are equipped with inner reflective surfaces so to both cut off light and redirect said light back onto target area 5 so it is not absorbed or otherwise wasted.
There are limitations to the approach illustrated in FIGS. 1A-C. For example, the adjustment of fixture 4 relative to pole 6 and addition of a visor may adversely affect the fixture's effective projected area (EPA) which may increase wind loading. An increased EPA may require a more substantial pole or more robust means of affixing the fixture to the pole, both of which may add cost. Given that a typical wide area or sports lighting application utilizes multiple poles with many fixtures per pole—see, for example, aforementioned U.S. Pat. No. 7,458,700—the added cost from even a slight change to EPA can be substantial.
As another example, the approach in FIGS. 1A-C is most appropriate for fixtures containing a single light source such as the high wattage HID lamps used in the aforementioned U.S. Pat. Nos. 7,458,700 and 7,789,540. It is well known that there is a need in the industry to create more efficient lighting fixtures; efficient in the sense that the fixtures themselves get more light out of the fixture housing and onto the target area, and in the sense that the light sources themselves are more compact while demonstrating a comparable or higher efficacy. This poses a problem because when multiple smaller light sources (e.g., LEDs) are housed in fixture 4, a single visor may not adequately redirect all spill light back onto target area 5 or provide a distinct cutoff; this can result in uneven illumination, shadowing effects, or glare which can be a nuisance or potentially dangerous (e.g., affecting playability on the field).
Accordingly, there is a need in the art for a design of lighting fixture which can realize the benefits of multiple smaller light sources such as LEDs (e.g., long life, high efficacy, ability to aim to multiple points, greater flexibility in creating lighting uniformity, etc.) while preserving desirable features of said fixture (e.g., low EPA, high coefficient of utilization, etc.), and a method of operating such so to address the lighting needs of a target area while avoiding undesirable lighting effects (e.g., uneven illumination, shadowing effects, glare, etc.).